Systems and methods for multicarrier transceiver with radio frequency interference reduction

ABSTRACT

A multi-carrier information transceiver that exhibits robustness against radio frequency interference (RFI) signals present in the communications channel. The transceiver includes a RFI mitigation technique that operates not only during the steady state operation of the transceiver but also during the training stage of the transceiver. That requires dynamically modifying the training signals when the presence of RFI is detected. The modification of the training signals facilitates the estimation of RFI, improving the performance of the multi-carrier transceiver.

RELATED APPLICATION DATA

This application claims the benefit of U.S. Provisional Application Ser.No. 60/210,556 entitled “Methods to Improve the Performance of DSL inthe Presence of RFI” filed Jun. 9, 2000 and incorporated herein byreference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to information transceivers. In particular, thisinvention relates to multi-carrier information transceivers with radiofrequency interference reduction.

2. Description of Related Art

Multi-carrier communications transceivers allow the high-speedtransmission of information using the twisted-pair telephone lines thatconnect individual subscribers to a telephone central office. Each pairof copper wires provides a communication channel in which the frequencyresponse attenuates as the frequency increases. The wires also containnoises of a different nature produced by a variety of sources. Amongthese noises are thermal noises produced by electric devices andcross-talk noises produced by, for example, other subscribers connectedto the same central office and sharing the same bundle of twisted-pairs.

The twisting of the twisted-pairs help to reduce the cross-talk noise bylimiting electromagnetic coupling between the pair of lines that areclose together. However, as the frequency of operation increases, theeffect of twisting is limited and the cross-talk noise increasesproportional to frequency.

In order to provide reliable communications over a channel with limitedbandwidth and frequency-dependent noise, multi-carrier transceiversapply a “divide and conquer” strategy. In this strategy, the totalbandwidth of the communication channel is divided into a number offrequency sub-bands. Each sub-band is a sub-channel in which aninformation signal is transmitted. The width of the frequency sub-bandsis chosen to be small enough to allow the distortion introduced by asub-channel to be modeled by a simple complex value representing theattenuation and phase shift of the received signal. Various informationsignals are transmitted simultaneously using the various sub-channels.The receiver is able to separate the information signals in thedifferent frequency sub-bands by using a bank of band-pass filters eachone tuned to one of the different sub-bands. If these filters are chosenproperly, the noise in each frequency band can be modeled using only thenoise level present in that sub-band, with the noise in one band havinglittle to no effect in the adjacent sub-bands.

A primary advantage of a multi-carrier transceiver is that thetransceiver parameters can be optimized for different channel conditionsin order to obtain maximum performance. The optimization process can besummarized as follow: First, a desired bit error rate is established.Second, the signal-to-noise ratio available in every sub-channel ismeasured. The bit error rate and the signal-to-noise ratio are then usedto determine the maximum bit transmission rate that the sub-channel cansupport. Finally, an optimal set of information signals capable oftransmitting this maximum bit transmission rate is found. By optimizingeach sub-band, the total transmission capacity of the multi-carriertransceiver for a given error rate is maximized.

Usually, the noise in the telephone lines also contains radio frequencyinterference (RFI) produced by, for example, electromagnetic coupling ofradio frequency signals coming from radio broadcasting transceivers thatoperate in the same radio frequency band as the multi-carriertransceiver. When present, this RFI can degrade the performance of themulti-carrier transceiver significantly, making the multi-carriertransceiver operate well below its optimum performance. The nature ofthe RFI is different from the difficulties associated with thermal noiseand crosstalk noise. Optimizing a transceiver to operate in the presenceof all the noises results in transceivers with great complexity, such asthe transceiver disclosed by Sandberg et al. in 1995 entitled“Overlapped Discrete Multitone Modulation for High Speed Copper WireCommunications.” In practice, RFI mitigation techniques that minimizethe degradation in performance are preferred.

SUMMARY OF THE INVENTION

For ease of illustration the following terminology will be used todiscuss the operation of an exemplary multi-carrier transceiver.Specifically, an idle channel is a communications channel that maycontain noise, crosstalk and RF signals in any portion of the spectrum,but does not contain upstream or downstream multi-carrier signals. Thecarriers in the multi-carrier transceiver will be denoted as tones. Atone is disabled when there is no energy transmission in that particulartone. A training or initialization signal, which is typically sentduring the training state, is a multi-carrier transceiver initializationtraining signal used to train the transceiver before commencing thetransmission of information. For the multi-carrier transceiver known asADSL, these training signals are defined in the INITIALIZATION sectionof ITU standards G.992.1 (G.dmt), G.992.2 (G.lite) and the G.994.1(G.hs), incorporated herein by reference in their entirety.

Steady state signals or information signals are the signals sent by themulti-carrier transceiver when communicating information data bits. Thesteady state transmission typically follows the training statetransmission. For the multi-carrier transceivers known as ADSL, thesteady state signals are defined in the SHOWTIME sections of ITUstandards G.992.1 (G.dmt) and the G.992.2 (G.lite), incorporated hereinby reference in their entirety.

An RFI band is a group of one or more tones in which a single RFI isidentified. In general, the location of these bands within the totalbandwidth of transmission is not known until the operation of themulti-carrier transceiver starts; and the tones in an RFI band may ormay not be disabled during the transceiver operation. However, there arecertain restricted RFI bands where the presence of RFI is highlyprobable. The location of these restricted RFI bands can be specified inadvance before the operation of the multi-carrier transceiver starts,and, for example, the tones in a restricted RFI band permanentlydisabled during the operation of the transceiver.

RFI can, for example, be one of the many performance limiting factorswhen a multi-carrier transceiver is deployed in the field. For themulti-carrier transceiver known as ADSL, tests that include measuringthe performance of ADSL in the presence of RFI are now being defined in“G.test.bis: Laboratory Set-ups and procedures to include RFIimpairments in the testing of DSL transceivers” by Nortel Networks®,incorporated herein by reference in its entirety. These tests, as wellas other industry-standard tests, provide a good reference model inwhich the performance RFI mitigation techniques can be measured.

An exemplary embodiment of the present invention describes amulti-carrier information transceiver with robustness against radiofrequency interference (RFI) signals present in a communicationschannel. The multi-carrier transceiver comprises a radio frequencyinterference mitigation technique that operates, for example, not onlyduring the steady state operation of the transceiver but also during thetraining state of the transceiver.

The transceiver is able to dynamically modify the training signals whenthe presence of RFI is detected. For example, the training signals canbe modified by dynamically disabling tones in the region of the spectrumwhere the RFI is detected. For example, this detection can occur duringan initialization phase. In this exemplary embodiment, the receiversends a message instructing the transmitter to disable tones in themulti-carrier signals during certain phases of training and or steadystate operation. The message contains, for example, a field thatdesignates which of the tone number(s) are to be disabled and duringwhich stages of training and/or steady state operation they are to bedisabled. The transmitter can also receive this message and, forexample, disable the specified tones during the specified stages oftraining and or steady state, for example, during a signal-to-noiseratio measurement and related calculations, during a training of theequalizer, or in other types of training or measurement. During theremaining stages of training and/or steady state, where instructions arenot necessarily specified in the message, the transmitter does notdisable the specified tones, but could send the standard signals inthose tones.

According, an in accordance with an exemplary embodiment of thisinvention, a first aspect of the invention relates to providing animproved multi-carrier transceiver.

Aspects of the invention also relate to providing a multi-carrierinformation transceiver in which, for example, prior to the trainingphase, the presence or absence of RFI in the communications channel canbe established. If, for example, RFI is detected, the receiver caninstruct the transmitter to disable tones in one or more of the trainingsignals, and during different stages of the modem training phase. Thereceiver can also instruct the transmitter to disable tones in theinformation signals during the steady state phase. If no RFI isdetected, then, for example, the transmission of both training andsteady state signals can occur without disabling any tones.

Aspects of the invention also relate to providing a multi-carrierinformation transceiver in which a RFI mitigation technique takesadvantage of the disabled tones in both the training signals and thesteady state signals to better estimate the RFI.

These and other features and advantages of this invention are describedin, or are apparent from, the following detailed description of theembodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an exemplary multi-carriertransceiver according to this invention;

FIG. 2 is a flowchart illustrating the exemplary operation of thefrequency-domain RFI mitigation device according to this invention;

FIG. 3 is a flowchart illustrating an exemplary method of creating atemplate according to this invention;

FIG. 4 shows an example of a set of templates according to thisinvention;

FIG. 5 is a flowchart illustrating an exemplary method of performing RFIinitialization according to this invention;

FIG. 6 is a flowchart illustrating a method of RFI mitigation duringtransceiver training according to this invention;

FIG. 7 illustrates an exemplary RFI detection/estimation for an idlechannel with noise and a number of RFI bands according to thisinvention;

FIG. 8 illustrates an exemplary composite RFI estimate determined usingan exemplary method according to this invention;

FIG. 9 is a flowchart illustrating an exemplary method of time-domainwindowing according to this invention; and

FIG. 10 illustrates an exemplary time-domain windowing operationaccording to this invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates an exemplary multi-carrier transceiver 100.Specifically, the transmitter section of one transceiver and thereceiving section of a second transceiver are shown in FIG. 1. Themulti-carrier transceiver 100 comprises a transmitter section 200 and areceiver section 300 interconnected by communications channel 120 andlinks 5. The transmitter 200 comprises a clock 210, a controller 220, asymbol generator 230, a tone manager 240, a memory 250, a frequencydomain to time domain converter 260, a memory 270, a digital to analogconverter 280 and a filter 290 interconnected by link 5. The receiver300 comprises a filter 310, an analog to digital converter 320, a memory330, a time-domain RFI mitigation module 340, a time domain to frequencydomain converter 350, a frequency domain RFI mitigation module 360, amemory 370, an equalizer 380, a memory 390, a symbol decoder 400, aclock 410 and a controller 420 interconnected by link 5.

While the exemplary embodiment illustrated in FIG. 1 shows thetransceiver 100 and associated components collocated, it is to beappreciated that the various components of the transceiver 100 can belocated at distant portions of a communications network. Thus, it shouldbe appreciated that the components of the transceiver 100 can becombined into one device or separated into a plurality of devices.Furthermore, it should be appreciated that for ease of illustration, thevarious functional components of the transceiver 100 have been dividedas illustrated in FIG. 1. However, any of the functional componentsillustrated in FIG. 1 can be combined or further partitioned withoutaffecting the operation of the system. As will be appreciated from thefollowing description, and for reasons of computation efficiency, thecomponents of the document can be arranged at any location within acommunications network without effecting the operation of the system.Furthermore, it is to be appreciated that the term module as used hereinincludes any hardware and/or software that provide the functionality asdiscussed herein. Furthermore, the links 5 can be a wired or wirelesslink or any other known or later developed element(s) that is capable ofsupplying and communicating data to and from the connected elements.

In operation, the transmitter 200 codes input data 105 for transmissionon a communication link 120. The receiver 300 decodes the data receivedfrom the transmitter 200 and outputs the decoded data as output data110. In particular, the symbol generator 230 receives a portion of theinput data 105, such as a stream of data. The tone manager 240determines, with the aid of controller 220, which tones are enabled ordisabled based on, for example, channel conditions, noise, interference,or the like. The number of different values a symbol can take willdepend on, for example, the characteristics of the communicationschannel 120, the desired robustness of information transmission, or thelike. More specifically, the number of different values a symbol cantake depends on the signal-to-noise ratio available in a particularsub-channel and the desired bit error probability. When the controller220 determines that N bits have been received by symbol generator 230,the controller 220 instructs the symbol generator 230 to convert the runof received data bits into M symbols S₁, S₂, . . . , S_(M) which arestored in the memory, such as a register 250. The symbols in theregister 250 are assigned to tones in the multi-carrier transceiver.However, if a tone is disabled, the tone manager 240 does not assign asymbol.

For ease of illustration, the transceiver 100 treats the symbols S_(i)as if they were the amplitude of a signal in a narrow frequency band. Itis assumed that the phase deviation of each signal is zero when thesignal enters the communication link 120. Thus, the frequency domain totime domain converter 260 determines, with the aid of controller 220 andclock 210, a time-domain signal denominated multi-carrier symbol havingvalues X_(i). The X_(i) signal has its frequency components weighted bythe individual symbols S_(i) over the time period represented by the Msamples X_(i). The X_(i) signal values are then stored in the memory270. The contents of the memory 270 represent, in digital form, the nextsegment of the signal that is to be actually transmitted over thecommunication link 120. For the multi-carrier transceiver known as ADSL,a segment of the final portion of X_(i), denominated a cyclic prefix(CP), is prefixed to the multi-carrier symbol X_(i) itself, prior to theD/A conversion. The actual transmission of the digital signal isaccomplished by clocking the digital values onto communication link 120after converting the values to analog voltages using the D/A converter280. The clock 210 provides the timing pulses for the operation. Theoutput of the D/A converter 280 is low-pass filtered by the filter 290before being placed on the communications link 120.

The communications link 120 will, in general, both attenuate and phaseshift the signal represented by the X_(i). The communications link 120will also add noises, such as, thermal noise, crosstalk and RFI to thesignal output by the transmitter 200. At the receiving end ofcommunications link 120, an attempt to recover each S_(i) is made byessentially reversing the modulation process done by the transmitter 200and correcting for losses in the communications link 120.

Upon receipt of the signal at the receiver 300 from the transmitter 200,the via the communications link 120, the filter 310 low-pass filters thesignal to reduce the effects of out-of-band noise. Then, with thecooperation of the controller 420, the signals are digitized by A/Dconverter 320 and shifted, as X'_(i), into the memory 330, such as aregister. This is preferably accomplished with the aid of the clock 410,which can be synchronized to the clock 210. When M values have beenshifted into the register 330, the contents thereof are processed by thetime-domain RFI mitigation module 340, which multiplies the receivedsignal composed of CP and X'_(i) by a window in order to reduce thesidelobes of the RFI. The output of time-domain RFI mitigation module340 is converted, via a time-domain to frequency-domain converter 350into a set of frequency-domain samples. This transformation is theinverse of the transformation generated by frequency-domain totime-domain converter 260. The frequency-domain samples at the output ofthe converter 350 are processed by the frequency-domain RFI mitigationmodule 360 to generate a set of frequency domain symbols Y_(i), in whichthe RFI component has been mitigated. Then, the equalizer 380 updateseach Y_(i) for attenuation and phase shifts that may have resulted fromthe communication over the communications link 120 to recover a noisyversion S'_(i) of the original symbols. These symbols are then stored inthe memory, such as a buffer, 390. Finally, the contents of the memory390 are decoded by the symbol decoder 400 and output as the output datastream 110.

The RFI mitigation modules 340 and 360 attenuate the effects of the RFIin the communications channel 120, while the tone manager 240facilitates the operation of the frequency-domain RFI mitigation module360. The exemplary embodiments of the tone manager 240, the time-domainRFI mitigation module 340 and the frequency-domain RFI mitigation moduleare discussed below with references to FIGS. 2-10. However, thoseskilled in the art will readily appreciate that the description givenwith respect to these exemplary figures is for illustrative purposesonly.

For the purpose of this discussion, in relation to the frequency-domainRFI mitigation module 360 and the tone manager 240, the frequency-domainsignal values will be represented by bins in the Fast Fourier Transform(FFT). Each bin is a complex number representing the amplitude and phaseof a tone.

FIG. 2 is a flowchart illustrating an exemplary method of operation ofthe frequency-domain RFI mitigation module 360 according to anembodiment of the invention. In particular, control begins in step S200and continues to step S210. In step S210, an initialization step, atemplate is created. Next, in step S220, RFI initialization isperformed. Then, in step S230, the RFI is mitigated during thetransceiver training operations. Control then continues to step S240.

In step S240, RFI mitigation is performed during the transceiver steadystate operation. Control then continues to step S250 where the controlsequence ends.

The template creation step S210 can occur, for example, before thesystem is run for the first time. Thus, the templates must be created inadvance and, for example, stored in a memory. Alternatively, thetemplates can also be created off-line and pre-stored in a memory.

FIG. 3 is a flowchart illustrating an exemplary method of the templatecreation process according to an embodiment of the invention.Specifically, control begins in step S300 and continues to step S310. Instep S310, the shape of the time-domain window which will be used toconstruct the template is determined. Next, in step S320, the frequencyused to construct the window is determined. Then, in step S330, atime-domain pass-band window is determined in accordance with A(t) COS(fT). Control then continues to step S340.

In step S340, the frequency-domain representation of the pass-bandwindow is determined. Next, in step S350, the amplitude of the pass-bandwindow is normalized resulting in the desired template. Then, in stepS360, the template is stored. Control then continues to step S370 wherethe control sequence ends.

The stored templates can then be used to estimate the RFI during themitigation process. In particular, FIG. 4 illustrates an exemplary setof 10 templates having a size of 31 created according to an embodimentof the invention. However, in general any number of templates can bestored based on, for example, the accuracy of the estimate desired forthe RFI.

FIG. 5 is a flowchart illustrating in greater detail the RFIinitialization step S220 in greater detail. In particular, controlbegins in step S500 and continues to step S510. In step S510, the idlechannel is detected. Specifically, the receiver measures the idlechannel, which may contain noise, crosstalk and RFI signals in anyportion of the spectrum, but not upstream or downstream multi-carriersignals. However, it is to be appreciated that the channel does notnecessarily need to be idle. The channel could contain, for example,multi-carrier training signals as well as noises of different nature.Next, in step S520, the RFI bands are detected. Specifically, using thedata obtained from step S510, the receiver establishes the presence ofRFI bands and their locations. However, it is to be appreciated that ingeneral the detection of the RFI bands can be accomplished using avariety of criteria, such as the peak-to-average ratio, or the like.Likewise, more accurate detection can be accomplished at the expense ofmore complex criteria. Control then continues to step S530.

In step S530, an RFI mask is determined. In particular, a mask isconstructed in which all the values are one, except the three maskvalues centered on each RFI bin which are zeroed. However, in general,the number of values can be altered with the trade-off being the morevalues providing better template estimation at the expense of reducingthe number of carriers. Next, in step S540, the size of templates isdetermined. Since the RFI bands can be located near the beginning of theFFT or close to the end of the FFT, the templates used for those RFIbands may need to be shortened to conform to the size of the FFT. Then,in step S550, the filling segments are determined. Based on thepositions of the RFI bins and the lengths of the templates, the fillingsegments containing zeros are constructed. Then, the templates aretranslated to a particular RFI position with the aid of these segments.Control then continues to step S560.

In step S560, the tones located in RFI bands are disabled. Specifically,the receiver can instruct the transmitter to disable the tones locatedin the detected RFI bands. More specifically, the receiver can send theRFI mask to the tone manager. In an exemplary embodiment of theinvention, the receiver can send a message instructing the transmitterto disable the tones in the signals during a certain phase of thetraining and/or the steady state. The message can contain a field thatdesignates which tone number(s), e.g., tone number 77, 78 and 79, are tobe disabled and during which phase(s), e.g., MEDLEY, REVERB1, etc, oftraining and/or steady state they are to be disabled. The tone managerwould then receive this message and would disable the specified tonesduring the specified phases of training and or steady state, forexample, during a signal-to-noise ratio measurement and relatedcalculations, during the training of the equalizer, or during othertypes of training and/or measurements. During the unspecified phases oftraining and/or steady state, the transmitter would not disable thespecified tones but would send the standard signals in those tones.

FIG. 6 is a flowchart illustrating RFI mitigation during the transceivertraining procedure according to an exemplary embodiment of theinvention. Specifically, FIG. 6 is outlines the steps of S230 in greaterdetail. Control begins in step S600 and continues to step S610. In stepS610, an FFT output vector is determined. This FFT vector is thefrequency-domain representation of a multi-carrier symbol containing atraining signal. Next, in step S620, the individual RFI estimates aredetermined. However, in general, the individual RFI estimate can bedetermined using a variety of methods. In the present invention the RFIestimate is based on a distance measured between a received signal and areference signal. The received signal is an individual RFI band in theFFT output vector and is one of the pre-stored templates scaled by thebin value at the center of the RFI band. The distance is measuredbetween the three center bins of the individual RFI band and the threecenter bins of each template. The scaled template that results inminimum distance is then chosen. However, in general; other forms ofreference signals are possible. For example, it is possible to determinethe reference signals using a pre-defined analytical function.Additionally, it is possible to select the template using a pre-storedmapping function or some other selection mechanism. Furthermore, manydistance definitions are possible with the trade off that some arebetter that others at the cost of complexity.

Next, in step S630, a determination is made whether more RFI bands arepresent in the FFT output vector. If more RFI bands are present, controljumps back to step S620. Otherwise control continues to step S640.

In step S640, a composite RFI estimate is determined. Then, using all ofthe individual RFI estimates, a composite sum is determined. Thecomposite sum is an RFI estimate of the total RFI in the FFT outputvector determined in step S610. Next, in step S650, the RFI mitigationoperation is performed by subtracting the composite RFI estimate fromthe received FFT output signal, thus mitigating the RFI effects in thetraining signals. Control then continues to step S660 where the controlsequence ends.

FIGS. 7 and 8 are examples of the RFI detection/estimation process.Specifically, FIG. 7 depicts the idle channel with noise and a number ofRFI bands. In particular, the FFT of one frame of noise at the output ofthe frequency domain RFI mitigation. Using this frame of noise, thedetection of RFI and the number of kFI bands can be established. Inorder to mitigate the RFI, the RFI is estimated. In particular, FIG. 8illustrates the composite RFI estimate determined using the exemplarymethod of this invention. The RFI estimate is formed using the strongestindividual RFI components, and it is subtracted from the originalreceived signal to mitigate the RFI effects.

The method of FIG. 6 can also apply to the RFI mitigation during thetransceiver steady state procedure according to an exemplary embodimentof the invention. Specifically, this corresponds to step S240 in greaterdetail. In particular, in step S610 a FFT output vector determined atthe output of the time domain to frequency domain converter is received.This FFT vector is the frequency-domain representation of amulti-carrier symbol containing a steady state signal. Next, in stepS620, the individual RFI estimates are determined. Then, in step S630 adetermination is made whether an RFI estimate for every RFI band in theFFT output vector has been determined. If more estimates are required,control jumps back to step S620. Otherwise, control continues to stepS640.

In step S640, the composite RFI estimate is determined. All theindividual RFI estimates are used to form a composite sum. The compositesum is an RFI estimate of the total RFI in the FFT output vectordetermined back in step S610. Next, in step S650, the RFI mitigationoperation is performed by subtracting the composite RFI estimate fromthe received FFT output signal, thus mitigating the RFI effects in thesteady state signals. Control then continues to step S660 where thecontrol sequence ends.

It is to be appreciated that from the above description, that in thisinvention the RFI mitigation can operate not only during the steadystate operation of the transceiver but also during the training state ofthe transceiver. This requires dynamically modifying the trainingsignals when the presence of RFI is detected.

FIG. 9 is a flowchart illustrating an exemplary operation of thetime-domain RFI mitigation module according to an embodiment of thisinvention. In particular, control begins in step S900 and continues tostep S910, In step S910, a signal including both the multi-carriersymbol X[k] and the cyclic prefix CP[k] is received. Next, in step S920,CP[k] is retained for use in the windowing operation. Then, in stepS930, the windowing is performed. Control then continues to step S940.

In step S940, the FFT of the windowed signal is determined. Control thencontinues to step S950 where the control sequence ends.

FIG. 10 illustrates an exemplary procedure used to realize the windowingoperation of step S930. Specifically, the windowing operation is appliedto the received signal Z[k] 1000, which consists of both the receivedmulti-carrier symbol X[k] 1020 and the complete cyclic prefix CP[k]1030. The operation can also be applied to X[k] and part of CP[k], bydiscarding the initial part of CP[k]. The example illustrated in FIG. 10depicts an embodiment in which the window W[k] 1040 is applied using thecomplete CP[k]. For example, assume that X[k] has 512 values, that CP[k]has 32 values, that Z[k] has 512+32=544 values and that W[k] has also544 values. The windowing operation consists of multiplying Z[k] byW[k], and then folding section 1-A into section 1-B, and folding section2-B into section 2-A.

The result of the windowing operation is denoted U[k] having 512 values.The expression for U[k] in terms of W[k] and Z[k] is:${U\lbrack k\rbrack} = \{ \begin{matrix}{{{{W\lbrack {16 + k} \rbrack}{Z\lbrack {16 + k} \rbrack}} + {{W\lbrack {17 - k} \rbrack}{Z\lbrack {528 + k} \rbrack}}},} & {{{{for}\quad k} = 1},\ldots\quad,16,} \\{{Z\lbrack {16 + k} \rbrack},} & {{{{for}\quad k} = 17},\ldots\quad,496,} \\{{{{W\lbrack {529 - k} \rbrack}{Z\lbrack {16 + k} \rbrack}} + {{W\lbrack {k - 496} \rbrack}{Y\lbrack {k - 496} \rbrack}}},} & {{{{for}{\quad\quad}k} = 497},\ldots\quad,512,}\end{matrix} $since W[k]=W[545−k], k=1,2, . . . ,32 by definition. Additionally,${U\lbrack k\rbrack} = \{ \begin{matrix}{{{{W\lbrack {16 + k} \rbrack}{Z\lbrack {16 + k} \rbrack}} + {( {1 - {W\lbrack {16 + k} \rbrack}} ){Z\lbrack {528 + k} \rbrack}}},} & {{{{for}\quad k} = 1},\ldots\quad,16,} \\{{Z\lbrack {16 + k} \rbrack},} & {{{{for}\quad k} = 17},\ldots\quad,496,} \\{{{( {1 - {W\lbrack k\rbrack}} ){Z\lbrack {512 + k} \rbrack}} + {{W\lbrack k\rbrack}{Z\lbrack k\rbrack}}},} & {{{{for}{\quad\quad}k} = 1},\ldots\quad,16,}\end{matrix} $since W[k]+W[33−k]=1, k=1,2, . . . ,16 by definition. To save multiplyoperations: ${U\lbrack k\rbrack} = \{ \begin{matrix}{{{{W\lbrack {16 + k} \rbrack}( {{Z\lbrack {16 + k} \rbrack} - {Z\lbrack {528 + k} \rbrack}} )} + {Z\lbrack {528 + k} \rbrack}},} & {{{{for}\quad k} = 1},\ldots\quad,16,} \\{{Z\lbrack {16 + k} \rbrack},} & {{{{for}\quad k} = 17},\ldots\quad,496,} \\{{{{W\lbrack k\rbrack}( {{Z\lbrack k\rbrack} - {Z\lbrack {512 + k} \rbrack}} )} + {Z\lbrack {512 + k} \rbrack}},} & {{{{for}{\quad\quad}k} = 1},\ldots\quad,16.}\end{matrix} $Notice that in the absence of noise, U[k]=X[((k−16))], i.e., U[k], isequal to a cyclically shifted version of X[k].

As illustrated in FIG. 1, the multicarrier information transceiver andrelated components can be implemented either on a DSL modem, such as anADSL modem, or separate programmed general purpose computer having acommunication device. However, the multicarrier information transceivercan also be implemented in a special purpose computer, a programmedmicroprocessor or a microcontroller and peripheral integrated circuitelement, an ASIC or other integrated circuit, a digital signalprocessor, a hardwired or electronic logic circuit such as a discreteelement circuit, a programmable logic device, such as a PLD, PLA, FPGA,PAL, or the like, and associated communications equipment. In general,any device capable of implementing a finite state machine that is inturn capable of implementing the flowcharts illustrated in FIGS. 2-3,5-6 and 9 can be used to implement the multicarrier informationtransceiver according to this invention.

Furthermore, the disclosed method may be readily implemented in softwareusing object or object-oriented software development environments thatprovide portable source code that can be used on a variety of computers,work stations, or modem hardware and/or software platforms.Alternatively, disclosed multicarrier information transceiver may beimplemented partially or fully in hardware using standard logic circuitsor a VLSI design. Other software or hardware can be used to implementthe systems in accordance with this invention depending on the speedand/or efficiency requirements of this system, the particular function,and the particular software and/or hardware systems or microprocessor ormicrocomputer systems being utilized. The multicarrier informationtransceiver illustrated herein, however, can be readily implemented in ahardware and/or software using any known later developed systems orstructures, devices and/or software by those of ordinary skill in theapplicable art from the functional description provided herein and witha general basic knowledge of the computer and telecommunications arts.

Moreover, the disclosed methods can be readily implemented as softwareexecuted on a programmed general purpose computer, a special purposecomputer, a microprocessor and associated communications equipment, amodem, such as a DSL modem, or the like. In these instances, the methodsand systems of this invention can be implemented as a program embeddedin a modem, such as a DSL modem, or the like. The multicarrierinformation transceiver can also be implemented by physicallyincorporating the system and method into a software and/or hardwaresystem, such as a hardware and software system of a multicarrierinformation transceiver, such as an ADSL modem, VDSL modem, networkinterface card, or the like.

It is, therefore, apparent that there has been provided in accordancewith the present invention, systems and methods for a multicarrierinformation transceiver. While this invention has been described inconjunction with a number of embodiments, it is evident that manyalternatives, modifications and variations would be or are apparent tothose of ordinary skill in the applicable art. Accordingly, applicantsintend to embrace all such alternatives, modifications, equivalents andvariations that are within the spirit and the scope of this invention.

1. A multi-carrier modulation transceiver comprising: a tone manager;and a multi-carrier transmitter that disables one or more tones duringat least one training state based on a received tone disable message. 2.The transceiver of claim 1, wherein the one or more tones are disabledto assist in determining impairments in a communications channel.
 3. Thetransceiver of claim 2, where the impairment is one of radio frequencyinterference and communications channel noise.
 4. The transceiver ofclaim 1, wherein the one or more tones can be disabled during a datacommunication state.
 5. The transceiver of claim 1, further comprisingone or more templates that are used to estimate radio frequencyinterference.
 6. The transceiver of claim 1, wherein one or moretemplates model radio frequency interference and are dynamically chosenfor one or more discrete multi-tone symbols.
 7. The transceiver of claim1, further comprising a symbol generator and a frequency domain to timedomain converter.